This invention relates generally to dental compositions and more particularly to dental cements based on dimer and trimer acids.
Researchers, in a quest for a non-eugenol cement, have demonstrated the ability of many non-chelating, monocarboxylic acids in a liquified state to form coherent, cementitious products on admixture with divalent metal oxides or hydroxides. The matrix of these monocarboxylate cements probably consists of a loose association of the divalent metallic carboxylate salt which, depending on the nature of the carboxylate anion, may have resinous or amorphous qualities (FIG. 1). Relatively high molecular weight monobasic acids yielded cements of low solubility and water-repellancy. However, probably because of the nature of the binder, these cements were mechanically weak, especially after exposure to water at 37.degree. C.
By contrast, the conventional polycarboxylate-based cements (i.e. zinc polycarboxylate and glass ionomer cements) derived from aqueous solutions of poly(alkenoic) acids and basic inorganic powders with leachable polyvalent cations, are much stronger materials. The matrices of these cements, which contain considerable amounts of water, are formed primarily by a series of ionic cross-linking reactions involving the pendant carboxyl groups of the polyelectrolyte and polyvalent cations displaced from the base powder by the acid solution. The resulting polymeric binders are relatively rigid and hydrophilic, i.e. they are stiff hydrogels (FIG. 2).
In U.S. Pat. Nos. 3,837,865 and 4,161,410, both to Pellico, a C.sub.36 dimer acid or a C.sub.54 trimer acid is mixed with zinc oxide or a mixture of zinc oxide and MgO to produce a dental composition. Powder to liquid ratios of up to 4 are disclosed. Because of these low powder to liquid ratios (P/L), the substances were somewhat flexible and not suitable for all dental cement applications. At higher P/L ratios, brittle fracture was expected. Furthermore, the compositions of Pellico and most dental compositions tend to contract upon setting. This contraction present serious difficulties when the cement is intended for many dental applications.